Here is how I did my 22.5" FleXcap front prototypes:
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First I had a standard 22.5" front rim. I took some measurements and draw a 3D model what I wanted the hubcaps to look like. Attaching idea was the same as in rear wheel version. After this I printed a Y0 section in 1:1 to paper.
Now the problem was how to manufacture easiest way that round elliptic shape. First idea was to use lathe and wood but I dont have that machine on home. Next idea was that I will use clay, because it is cheap and easy tool. However there was one problem that the size of that hubcap was so big that it would not fit to normal potterswheel.
Then the idea came that I can leave the part on table and rotate the shape. I cutted the Y0 section to 16mm thick wood. I also cutted round wood to match the heigth of the part. For base I had a plastic sheet where I drow a round circle of the current rear hubcap model. Marked the centerpoint and drilled a small hole there. After this I put the round wood over the center hole and drilled a skrew to it under the plastic. After this I rotated the wood under the table with powerdrill. Ot the top side I marked the center of the round wood by marker pen. Now I could attach the Y0 wood section to center of that Z-axis.
After this I just started to put some cly over the plastic and every time there were too much clay the woodpiece sweeped the exessive material out. After about 30 minutes I had got into this phase:
After this I just filled the centerhole and applied 5 layers of 300g twill glassfiber and polyester resin. I dont have to apply release agent because glasfiber dont attach to plastic. After a two hours of curing the glasfiber part was ready for cooling holes and cutting of the outer edges. Now when I draw the outer edged to the plastic they were copied to that glasfiber part also so it was easy to cut the outer edge. Cooling holes with holedrill and the prototype was ready for assembly tests.
Shape worked well but the cooling holes need more testing with plastic prototypes. My glasfiber part became too stiff compared to plastic. I could have taken other part of that clay tool with little restauring but I was only testing the basic shape. The used caly can be quite soft but not too soft. The tool broke up where the clay was most softest due to water etc...
Same method can be applied to all elliptic parts
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After this I will take a glasfiber mold out of that part for vacuumforming. Costs for vacuumforming tool are under 50 in this case because the glasfiber materials are free for me. Oherwise the cost would be something like this:
Clay 16
Polyester resin 1 liter + hardener 12
Normal glasfiber mat 3 layer about 15 (if 5x 300g twill about 50)
paint brush and gloves etc 3
plastic sheet about 10
Materials prices depend on where you buy them and how much...
So total cost about 55 (90) without the tools being used
. If you want that same tool to be CNC milled to wood it would cost about 1000.